<!DOCTYPE html>
<title>CSS Anchor Positioning: Invalidation from changing the base style</title>
<link rel="help" href="https://drafts.csswg.org/css-anchor-position-1/">
<link rel="help" href="https://issues.chromium.org/issues/333608683">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
  @position-try --pt {
    width: 50px; /* Undo force overflow */
  }
  #cb {
    position: relative;
    width: 200px;
    height: 200px;
    border: 1px solid black;
  }
  #anchor {
    position: absolute;
    left: 75px;
    top: 75px;
    width: 50px;
    height: 50px;
    background: coral;
    anchor-name: --a;
  }
  #anchored {
    position: absolute;
    position-anchor: --a;
    position-try-fallbacks: --pt flip-start;
    inset: 0;
    top: anchor(top);
    bottom: anchor(bottom);
    right: calc(anchor(left) + 5px);
    width: 50px;
    height: 50px;
    background: skyblue;
    justify-self: end;
  }
  #anchored.flip {
    background: seagreen;
    width: 300px; /* Force overflow */
  }
</style>
<div id=cb>
  <div id=anchor></div>
  <div id=anchored></div>
</div>
<script>
  test(() => {
    // Initially to the left.
    assert_equals(anchored.offsetLeft, 20);
    assert_equals(anchored.offsetTop, 75);

    // Flips to the right.
    anchored.classList.toggle('flip');
    assert_equals(anchored.offsetLeft, 75);
    assert_equals(anchored.offsetTop, 20);

    // Flips to the original position.
    anchored.classList.toggle('flip');
    assert_equals(anchored.offsetLeft, 20);
    assert_equals(anchored.offsetTop, 75);
  }, 'The chosen position fallbacks changes when the base style differs');
</script>
